1. Field of the Invention
The present invention relates to a potential sensor for inspecting a liquid crystal panel used in a television, a personal computer or the like.
2. Description of the Related Art
Typically, as a method for evaluating a liquid crystal panel, there are an operation test, a reliability test, an appearance test and the like. The above-mentioned inspection of the liquid crystal panel is mainly carried out as a lighting operation check test after a product is assembled. The higher speed of the inspection is required in conjunction with the larger size and the higher accuracy of the liquid crystal panel.
FIG. 1 is a view showing a conventional method for inspecting a liquid crystal panel. Traditionally, as the method for inspecting the liquid crystal panel, for example, a probe method is employed which makes respective probes 32, 31 come into contact with a gate voltage wiring 33 and a source voltage wiring 35 that are connected to a TFT transistor 30, as shown in FIG. 1, and then inspects a disconnection, a short-circuit or the like of a pixel electrode 2 based on its output voltage. This inspecting method detects a defect of the pixel electrode 2 of a liquid crystal panel 9 by applying an inspection signal to the source voltage wiring 35 and the gate voltage wiring 33 of the liquid crystal panel 9.
However, the above inspecting method has the problems, such as an increase in a contact error or an increase in a maintenance cost of the probes 32, 31. Moreover, a larger amount of display information requires a larger size, a full color and a higher minuteness of a liquid crystal display, which results in the problem of the higher speed of the inspection.
Japanese Laid Open Patent Application (JP-A-Heisei, 5-11000) discloses an active matrix array inspection apparatus as described below. The active matrix array inspection apparatus is provided with: a gate signal generator; a source signal generator; a gate signal line selector for selectively switching and connecting each gate signal line of an active matrix array to be inspected, to any of an output terminal, an open terminal and a ground terminal of the gate signal generator; a source signal line selector for selectively switching and connecting each source signal line of the active matrix array to be inspected, to any of an output terminal, an open terminal and a ground terminal of the source signal generator; a non-contact probe for detecting an electric condition of a drain terminal of a thin film transistor connected to the gate signal line and the source signal line at a non-contact condition; and a judging device for judging the acceptance or rejection of the thin film transistor on the basis of the detection output from the non-contact probe.
The present invention is accomplished in view of the above mentioned problems. Therefore, an object of the present invention is to provide a potential sensor for detecting a voltage of an inspection target at a non-contact condition to attain a higher speed of an inspection.
In order to achieve an aspect of the present invention, a potential sensor, includes: a field effect transistor; a power supply supplying a direct current voltage to a gate electrode of the field effect transistor; and a switching device switching between connecting the gate electrode to the power supply and disconnecting the gate electrode from the power supply, and wherein when the gate electrode connected to the power supply, the field effect transistor is in action, and when the gate electrode is disconnected from the power supply, the field effect transistor is in action.
In this case, when the gate electrode is disconnected from the power supply, the field effect transistor is in action with a charge included in an oxide film under the gate electrode.
Also in this case, the charge is charged in the oxide film when the gate electrode is connected to the power supply.
Further in this case, wherein when the potential sensor is used, the gate electrode is coupled through an air-gap to an inspection target.
In this case, a voltage is applied to the inspection target.
Also in this case, the air-gap has an interval of approximately 20 xcexcm.
Further in this case, when the gate electrode is connected to the power supply, the voltage applied to the inspection target is applied to the switching device not to be outputted in a source electrode of the field effect transistor.
In this case, when the gate electrode is disconnected from the power supply, the voltage applied to the inspection target is outputted in a source electrode of the field effect transistor not to be applied to the switching device.
Also in this case, the field effect transistor is an enhancement type MOS-FET.
In order to achieve another aspect of the present invention, a potential sensing method, includes: (a) providing a field effect transistor; (b) providing a power supply supplying a direct current voltage to a gate electrode of the field effect transistor; (c) providing a switching device switching between connecting the gate electrode to the power supply and disconnecting the gate electrode from the power supply; (d) applying a voltage to an inspection target; (e) coupling the gate electrode through an air-gap to the inspection target; (f) connecting the gate electrode to the power supply; (g) disconnecting the gate electrode from the power supply after the (f); and (h) outputting the voltage applied to the inspection target from a source electrode of the field effect transistor while the (g) is performed.
In this cases the (f), (g) and (h) are performed repeatedly.
Also in this case, when each of the (f) and (g) is performed, the field effect transistor is in action.
Further in this case, when the (f) is performed, a charge from the power supply is charged in an oxide film under the gate electrode.
In this case, the when the (g) is performed, the field effect transistor is in action with the charge included in the oxide film.
Also in this case, the (e) includes setting the air-gap to have an interval of approximately 20 xcexcm.
Further in this case, when the (f) is performed, the voltage applied to the inspection target is applied to the switching device not to be outputted from the source electrode.
In this case, when the (g) is performed, the voltage applied to the inspection target is not applied to the switching device.
Also in this case, the inspection target is a pixel electrode of a liquid crystal panel.
Further in this case, the field effect transistor is an enhancement type MOS-FET.
In this case, the (h) is performed in a condition that the gate electrode is not in mechanical contact with the inspection target.